Abstracts
Week of October 20, 2024
| Tea | Cookies |
3:30pm -
KT 8th Floor Lounge
|
Please join us for pre-seminar Tea |
| Group Actions, Geometry and Dynamics | Critical exponent gap |
4:15pm -
KT205
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We will discuss the following result. For every geometrically finite Kleinian group Γ < SL2(ℂ) there is εΓ such that for every g ∈ SL2(ℂ) the intersection gΓg-1 ∩ SL2(ℝ) is either a lattice or a has critical exponent δ(gΓg-1 ∩ SL2(ℝ)) ≤ 1-εΓ. This result extends Margulis-Mohammadi and Bader-Fisher-Milier-Strover. We will discuss some ideas of the proof. We will focus on the applications of a new ergodic component, of preservation of entropy in a direction. |
| Geometry, Symmetry and Physics | The Topological Part of the Period-Index Conjecture |
4:30pm -
KT 801
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The period-index problem is a classical problem about finite-dimensional division algebras over a field. When the base field is the function field of a complex variety, there is a longstanding conjecture, which is wide open for function fields of threefolds and beyond. I will discuss recent perspectives on the conjecture from topology, Hodge theory, and moduli theory. Finally, I will explain a result showing that, roughly speaking, topological solutions to the conjecture exist for complex function fields of arbitrary dimension.
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| Tea | Cookies |
3:30pm -
KT 8th Floor Lounge
|
Please join us for pre-seminar Tea |
| Geometry & Topology | Atoroidal surface bundles |
4:00pm -
KT 207
|
I will discuss recent work with C. Leininger in which we produce purely pseudo-Anosov surface subgroups of mapping class groups, obtaining the first compact atoroidal surface bundles over surfaces. We do this by constructing a type-preserving representation of the figure eight knot group into the mapping class group of the thrice-punctured torus. |
| Analysis | Pre-seminar: limiting absorption principle, manifolds with corners |
4:00pm -
KT 801
|
This is a 30min slow-pace pre-seminar discussion aiming to familiarise early-career researchers with basic ideas used in Thursday Analysis Seminar talk. The focus will be put on ideas, and technicalities are kept to a minimum. Topics include: limiting absorption principle, scattering theory, manifolds with corners. |
| Applied Mathematics | Instruction-Following and its Evaluation Using LLMs |
2:30pm -
LOM 214
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In this talk, I’ll discuss our recent works on evaluation instruction-following capabilities of LLMs. State-of-the-art LLMs are able to follow user instructions and perform tasks across a wide range of domains with impressive results. However, their performance on open-ended text generation tasks is often evaluated on specific benchmarks and in certain ways, leaving questions about their robustness, generalizability, and alignment with human expectations. First, I will discuss the difficulties with the evaluation of long-form text generation, especially in the context of text generation tasks such as summarization with nuanced differences. Second, I’ll discuss our new work on comprehensive and large-scale meta-evaluation of instruction-following. Our study reveals that instruction-controllable summarization remains challenging for LLMs: 1) LLMs evaluated still make factual and other types of errors in their summaries; 2) all LLM-based evaluation methods cannot achieve a strong alignment with human annotators. We found that open-source models like Llama-3.1-405B are approaching the performance of top proprietary models, and that evaluation protocols do not consistently outperform baseline pairwise comparison approaches. Moreover, protocol effectiveness varies significantly depending on the base LLM and dataset diversity. I hope to highlight some ongoing and interesting challenges and opportunities in refining LLMs in long-form generation tasks. |
| Tea | Cookies |
3:30pm -
KT 8th Floor Lounge
|
Please join us for pre-Colloquium Tea |
| Walter Feit Memorial Lecture | Geometry of the Eisenstein spectrum |
4:00pm -
KT 205
|
This will be a nontechnical talk about our work with David Kazhdan on the spectrum of the Laplace and Hecke operators in the span of Eisenstein series. This very classical problem in the spectral theory of automorphic forms goes back to at least Langlands, who also introduced the analytic techniques that allow to find the spectrum in principle. To replace an in-principle answer by a concrete answer, we found it very useful to have a certain geometric interpretation of the multivariate contour integrals in Langlands’ setup. My goal in this talk will be to explain this geometric interpretation. |
| Tea | Cookies |
3:30pm -
KT 8th Floor Lounge
|
Please join us for pre-seminar Tea |
| Analysis | Full asymptotics for Schrodinger wavepackets |
4:00pm -
KT 207
|
Since the work of Jensen–Kato, the analysis of the Schrodinger–Helmholtz equation at low energy has been used to study wave propagation in various settings, both relativistic and nonrelativistic. Recently, Hintz has used these methods to study wave propagation on black hole spacetimes. Part of Hintz’s result is the production of asymptotics in all possible asymptotic regimes, including all joint large-time, large-radii regimes. We carry out the analogue of this analysis for the Schrodinger equation. Based on joint work with Shi-Zhuo Looi. |
| Quantum Topology and Field Theory | Modular functor conjecture from quantum Teichmüller theory |
4:30pm -
KT 101
|
H Verlinde suggested in 1980’s to use quantization of the Teichmüller spaces of surfaces to study the spaces of conformal blocks for the Liouville conformal field theory. This suggestion initiated and stimulated the development of quantum Teichmüller theory, and the first major steps were taken by Kashaev and by Chekhov and Fock in 1990’s, where the Chekhov-Fock quantization is generalized later by Fock and Goncharov to quantization of cluster varieties. The modular functor conjecture asserts that these quantum theories of Teichmüller spaces indeed yield a 2-dimensional modular functor, which can be viewed as one axiomatization of conformal field theory. The core part of the conjecture says that, for each punctured surface S and an essential simple loop in S, the Hilbert space associated to S by quantum Teichmüller theory should decompose into the direct integral of the Hilbert spaces associated to the surface obtained by cutting S along the loop and shrinking the holes to punctures. I will give an introduction to this story and present some recent developments, including 2405.14727.
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| Friday Morning Seminar | Friday Morning Seminar |
10:00am -
KBT 801
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A relaxed-pace seminar on impromptu subjects related to the interests of the audience. Everyone is welcome. The subjects are geometry, probability, combinatorics, dynamics, and more! |